38
\$\begingroup\$

If the neutral wire carries current, why do many people believe that it's safe? I've heard "You can touch the neutral wire/bar in the breaker box and not get shocked. Only the hot can hurt you." If the circuit is complete and current is flowing, can't you receive a shock?

\$\endgroup\$
  • 14
    \$\begingroup\$ Because it takes no sides in war. It's also called the Switzerland Wire. \$\endgroup\$ – Passerby Jul 22 '13 at 22:31
  • 1
    \$\begingroup\$ This article on allaboutcircuits.com explains it well. \$\endgroup\$ – yesitsme Jun 9 '15 at 17:47
55
\$\begingroup\$

The neutral is NOT safe to touch.

When everything is working correctly, it should be at most a few volts from ground. However, and this is the big gotcha, if there is a break in the neutral line between where you are and where it is connected back to ground, it can be driven to the full line voltage. Basically in that case you are connected to the hot line via any appliances that happen to be on in that part of the circuit. Those can easily pass the few mA it takes to kill you.

This is not supposed to happen, but since failures can be lethal and costly, a extra layer of safety is built into the protocol and rules. It is irresponsible and needlessly risky to consider the neutral line safe.

This is why modern appliances either have two prongs and everything is insulated from the user, or three prongs and anything conductive the user can touch is connected to ground. In some past cases there have been appliances with polarized 2-prong plugs, but those are seriously frowned upon today. I don't think you're going to get UL approval for such a device unless it is fully insulated, in which case you shouldn't need a polarized plug.

\$\endgroup\$
  • 4
    \$\begingroup\$ +1, It's important these questions get answered properly. " .. or three prongs and anything conductive the user can touch is connected to ground." this is why is someone has modified a three prong plug it can be dangerous -> it's then possible to invert the plug. \$\endgroup\$ – placeholder Jul 22 '13 at 22:18
  • 4
    \$\begingroup\$ Appliances such as lamps typically have polarized plugs because of the possibility that the user might touch the threads of a bulb which is being inserted or removed. If the Edison-base socket were being designed today, it would be constructed in such a fashion that no part of the bulb's base would be exposed while it was electrically connected to anything, but neither bulbs nor sockets could be changed to achieve that while remaining compatible with the variety of bulbs and sockets in use. \$\endgroup\$ – supercat Jul 22 '13 at 22:30
  • 3
    \$\begingroup\$ In a sense, I think the idea is to ensure that people are to the extent possible at least two "faults" away from experiencing a harmful condition. The neutral wire SHOULDN'T be far from ground potential, and people SHOULDN'T be touching the neutral wire or anything connected to it (like a the base of a partially-inserted bulb) but neither condition in itself would be harmful. Since either condition would only be one "fault" away from causing harm, though, neither condition should be considered "safe". \$\endgroup\$ – supercat Jul 22 '13 at 22:33
  • \$\begingroup\$ Which is why I'm surprised the plugs we use in the US still exist. It's very easy to accidentally touch the metal blades when pulling out or inserting the thing. Why don't we have shrouds on them like say the C14 plug? Ugh. \$\endgroup\$ – Passerby Jul 23 '13 at 6:24
  • \$\begingroup\$ @Passerby: It would be possible to design an outlet with a built-in switch, such that the contacts would only be energized when the plug was fully inserted (contact reliability implies that the contacts themselves should be relatively shallow). I doubt that the number of harmful incidents involving partially-inserted plugs would be sufficient to justify the added expense in most cases, though a "safety outlet" might be a good thing to have in e.g. a child's room. \$\endgroup\$ – supercat Jul 24 '13 at 15:30
4
\$\begingroup\$

On a non degraded correctly wired installation the neutral wire is safe because it is at the same potential than the ground terminal.

It is true that it carries current but because there is no voltage difference from ground there is no current passing through when you touch it.

\$\endgroup\$
  • 6
    \$\begingroup\$ -1 for a potentially dangerous answer. You're not wrong just incomplete and here incompleteness is dangerous. - on edit, removed DV \$\endgroup\$ – placeholder Jul 22 '13 at 22:20
  • 2
    \$\begingroup\$ @rawbrawb Thank you for alerting me for that. I just modified my answer. \$\endgroup\$ – Bruno Ferreira Jul 22 '13 at 22:23
  • 3
    \$\begingroup\$ This is only true on a correctly-wired installation that has not degraded. All that is needed is a single break in the neutral, and you have full voltage on the neutral. \$\endgroup\$ – Eric Gunnerson Jul 24 '13 at 2:50
  • 1
    \$\begingroup\$ @EricGunnerson You are right. Modified. \$\endgroup\$ – Bruno Ferreira Jul 24 '13 at 9:32
  • \$\begingroup\$ It is not strictly true that neutral and ground has the same potential. You will generally measure a few volts. The higher the load on the system, the higher voltage drop, and therefore a higher potential difference between ground and neutral. I dont have any numbers but I expect typically 2 to 10 volts. \$\endgroup\$ – Mads Skjern Sep 7 at 4:42
0
\$\begingroup\$

Consider the small appliance with dc transformer power supply such as TV and all appliances that have adaptor or dc transformer. And refer with illustration given by this link . It shows that the primary coil in line 1 is connected to line 2 nothing less and no bargain. The line 1 is a hotline and line 2 is neutral or common line which was actually connected each other. That’s the main reason why the neutral wire is not safe to touch due to the current voltage flowing from one line to another and when can we touch the neutral wire while working? In The Philippines we usually connect the Neutral wire to the ground rod, purposely to make it zero volts wire or the green wire serve as ground should be connected to the appliance. As long as there is a turning coil of wire on your appliance in that particular circuit, the Neutral wire will not be safe to touch unless there is an intimate relationship with the ground.

\$\endgroup\$
0
\$\begingroup\$

It depends.

Under normal conditions the neutral is at close to earth potential but if the neutral goes open circuit then it can rise up to live potential and shock you. Similarly live and neutral could be reversed at some point in the supply system.

So the question then becomes "is the risk of a dangerous voltage on the neutral due to a break in the neutral wiring acceptable?". That is a question that is impossible to answer in the general case as it depends entirely on the circumstances.

On portable appliances I would always unplug before working. I would not consider plugs and sockets and thin flexible cables to be reliable enough to rely on the neutral remaining at earth potential.

On the other hand in the UK it is normal practice to work on circuits of an electrical installation where the neutral is not isolated. I don't know what practices are in other countries.

Going even further many power distribution systems combine the functions of neutral and earth. So do electrified railways.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.